Thanks! I will ask our CRM to enable window functions and give it a shot. However, the heat map card functionality is limited, and I don't think I will be able to include totals because you can only use 3 columns for the card.
I am facing the same issue. Can't figure out how to calculate subtotals for cohort users and averages for each retention time period. I am not good with R, I will try ti sign up for the Beta jupyter notebook to push the results directly into the heat map card. I don't believe the averages will show, though.